A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to make use of a lithographic apparatus as efficiently as possible, it is desirable to achieve a high throughput of the lithographic apparatus, so that a large amount of substrates can be processed by the lithographic apparatus in the shortest possible time.
In a scanning mode of a scanning-type lithographic apparatus, the substrate table is moved with a substrate table scanning movement, i.e. a movement with a substantially constant speed, across a projection system. At the same time as the scanning movement of the substrate table, a support supporting a patterning device is scanned also with a scanning movement, i.e. a movement with substantially constant speed across the projection system to impart a pattern in a radiation beam of the lithographic apparatus. Since during projection the support of the patterning device is moved from a starting position to an end position, the patterning device support has to be moved back to the start position before the patterning device support is ready for a new scanning movement in the same direction.
Therefore, the lithographic apparatus may be configured to make a meandering pattern of substrate table scanning movements over the substrate. The subsequent scanning movements of the patterning device support may then be in opposite directions, since the direction of the subsequent substrate scanning movements is also in opposite directions. For each substrate table scanning movement, the substrate table has to be decelerated and accelerated to obtain the desired speed and direction. Such deceleration and acceleration to a substantially constant speed takes considerable time.
In an alternative scanning trajectory, a substrate table scanning movement is made across multiple dies arranged in a row or column on the substrate, for example over the length of the substrate, while the patterned radiation beam is only projected on a part of the dies. For example, during a single substrate table scanning movement the patterned radiation beam is projected only on the dies at uneven locations of the row or column of dies. The time required for passing the dies at even locations is used to bring the patterning device support back from the end position to the start position.